The invention relates generally to battery powered electronic locking apparatus and deals more particularly with a control for indicating low battery voltage and reserving a portion of the battery's energy for operating the lock upon insertion of selected keys.
Battery powered electronic locks were previously known which include a red LED mounted on an outer housing of the lock to indicate low battery voltage or the insertion of an invalid card, and a green LED mounted on the outer housing to indicate a valid card and unlocked status of the lock. Upon insertion of a valid key card, the lock will be opened and the red LED will not be activated if the battery voltage is above a certain level, but activated if the battery voltage is below the certain level. This electronic lock is programmable during installation to provide such activation of the red LED either upon insertion of every valid key card or insertion of only those valid key cards associated with maintenance people. After each insertion of a valid key card subsequent to the battery voltage dropping to or below the certain level, the red LED is activated and the lock opened until the battery becomes so drained that it does not provide sufficient voltage to operate the lock.
There are two problems with this system. If the warning provided by the red LED is not noticed by a maintenance person, or if noticed, not heeded in time, the lock may not be capable of opening during an emergency situation. Also, the batteries of this type of electronic lock are accessible only from the inside of the door, and if the lock is rendered inoperable, such access may be precluded.
Another battery powered electronic lock is described in U.S. Pat. No. 4,148,092 to Martin. It briefly discloses a battery voltage indicating means which sounds an audio alarm when the battery voltage drops below a certain level, and allows access. The battery voltage indicating means is also supposed to maintain the lock open a given number of operations after the sounding of the alarm to prevent lock-out. The door will remain unlocked until a maintenance person changes the batteries, and this may not be desirable under many circumstances.
Accordingly, a general object of the present invention is to provide a control for a battery powered lock which indicates low battery voltage and reserves a portion of the battery's energy for operation of the lock upon insertion of maintenance, emergency, or other selected keys or key cards.